Try changing your USB cable as some cables do not support transferring data. If that does not solve your problem, contact us at support@blues.com and we will get you set up with another tool to communicate with the Notecard.
The help command gives more info.
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Meet Notecarrier CX - A Combined Notecarrier + STM32L4 Host MCU in One Board
Tutorials to help you get up and running with Blues hardware fast.